A320 CAPT APPROACHING HOLD SHORT LINE; IS DISTRACTED BY MASTER CAUTION AND CROSSES INADVERTENTLY.

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I WAS THE CAPT AND PNF. I LOADED THE FMS BRIDGE VISUAL RWY 28R IN THE PRIMARY FLT PLAN AND THE ILS RWY 28L IN THE SECONDARY FLT PLAN. PRIOR TO THE TOP OF DSCNT WE SPECIFICALLY BRIEFED THE MEL FOR ONE THRUST REVERSER INOP PROC; THE FMS VISUAL RWY 28R AND THE ILS RWY 28L APCHS; AND THE TAXI PLAN TO THE GATE FOR BOTH RWYS. AS WE STARTED DOWN ON THE RWY 28R APCH; WE WERE GIVEN SIDESTEP INSTRUCTIONS TO INTERCEPT THE VISUAL FOR RWY 28L. NOW ON THE RWY 28L APCH AND ABOUT 1700 FT WE WERE GIVEN NEW INSTRUCTIONS TO SIDESTEP ONCE AGAIN BACK TO VISUAL/ILS RWY 28R. I WAS THE PNF AND I MADE ALL THE FMS/MCDU CHANGES. THE FO LANDED ON RWY 28R AND AS WE WERE SLOWING DOWN; I GAVE HIM INSTRUCTIONS NOT TO TURN S ON EITHER RWYS 1L OR 1R AS WE DID NOT HAVE PERMISSION TO DO SO. AFTER XING RWY 1L WE WERE IN POS TO TURN L ON TXWY E (90 DEG L) BUT WERE THEN GIVEN INSTRUCTIONS BY THE TWR TO CONTINUE DOWN THE RWY AND TURN OFF ON THE HIGH-SPD (TXWY T) AND HOLD SHORT OF RWY 28L. I TOOK CTL OF THE ACFT AT THIS TIME AND THE FO ACKNOWLEDGED THE RWY 28L HOLD SHORT INSTRUCTIONS. AS I MADE THE TURN ONTO TXWY T; I LOOKED UP AND ACROSS RWY 28L AND ON THE S SIDE WAS AN ACR HVY TAXIING ON TXWY B APCHING TXWY T. THE FO AND I HAD PREVIOUSLY BRIEFED THE MEL FOR THRUST REVERSE SYS BEFORE LNDG AND WERE EXPECTING THE MASTER CAUTION LIGHT AND ECAM DISPLAY TO COME ON; BUT IT DID NOT COME ON DURING LNDG. AS WE WERE APCHING THE RWY 28L HOLD SHORT LINE; AT THIS CRITICAL MOMENT; THE MASTER CAUTION LIGHT CAME ON AND I LOOKED DOWN TO SEE WHAT THE MALFUNCTION WAS. AT THE SAME MOMENT; THE NOSE CROSSED OVER THE RWY 28L HOLD SHORT LINE. I REALIZED WE WERE OVER THE LINE AND ASKED THE FO TO CALL THE TWR AND TELL THEM WE WERE NOW STRADDLING THE RWY 28L HOLD SHORT LINE AND THE TWR INSTRUCTED LNDG TFC ON RWY 28L TO GO AROUND. WE BOTH HAD OUR TAXI DIAGRAM CHARTS OUT AND DISPLAYED.